rc/sh/confirm

#!/usr/bin/env sh
# YES_ZSH YES_BASH YES_DASH YES_ASH

### @ confirm
### display a simple yes-or-no prompt and return 0-or-1 respectively.
###
### ```
### $ confirm && echo yay || echo nay
### Continue? [y/N] y
### yay
### $ confirm && echo yay || echo nay
### Continue? [y/N] n
### nay
### ```
###
### a real world example:
###
### ```
### $ g1 && confirm && git commit -a --amend --no-edit
### daf84e3 document a ton of stuff
### Continue? [y/N] y
### [master 92bdf76] document a ton of stuff
###  Date: Sun Aug 1 09:27:25 2021 -0700
###  20 files changed, 406 insertions(+), 29 deletions(-)
### ```

if [ -n "$ZSH_VERSION" ]; then
    confirm() {
        [ $# -eq 0 ] || { printf "%s\n" "$0: too many arguments" >&2; return 2; }
        local c=
        read -q '?Continue? [y/N] ' c
        ret=$?
        echo >/dev/tty
        return $ret
    }
elif [ -n "$BASH_VERSION" ]; then
    confirm() {
        [ $# -eq 0 ] || { printf "%s\n" "$0: too many arguments" >&2; return 2; }
        local c=
        read -n1 -p "Continue? [y/N] " c 2>&1
        echo
        [ "$c" = y ] || [ "$c" = Y ]
    } 1<>/dev/tty <&1 # ensure this interacts with a terminal instead of a pipe
else
    confirm() (
        [ $# -eq 0 ] || { printf "%s\n" "$0: too many arguments" >&2; return 2; }
        old="$(stty -g)"
        trap 'stty "$old"' INT EXIT
        printf 'Continue? [y/N] '
        stty -icanon
        c="$(dd ibs=1 count=1 2>/dev/null)"
        echo
        [ "$c" = y ] || [ "$c" = Y ]
    ) 1<>/dev/tty <&1 # ensure this interacts with a terminal instead of a pipe
fi

[ -n "${preload+-}" ] || confirm "$@"